Over the years considerable work has been devoted to additives for controlling (preventing or reducing) deposit formation in the fuel induction systems of spark-ignition internal combustion engines. In particular, additives that can effectively control fuel injector deposits, intake valve deposits and combustion chamber deposits represent the focal point of considerable research activities in the field and despite these efforts, further improvements are desired.
Direct injection gasoline (DIG) technology is currently on a steep developmental curve because of its high potential for improved fuel economy and power. Environmentally, the fuel economy benefits translate directly into lower carbon dioxide emissions, a greenhouse gas that is contributing to global warming.
Conventional multi-port injection (MPI) engines form a homogeneous pre-mixture of gasoline and air by injecting gasoline into the intake port, while a direct injection gasoline engine injects gasoline directly into the combustion chamber like a diesel engine so that it becomes possible to form a stratified fuel mixture which is rich in the neighborhood of the spark plug but highly lean in the entire combustion chamber. Due to the formation of such a stratified fuel mixture, combustion with the overall highly lean mixture can be achieved, leading to an improvement in fuel consumption approaching that of a diesel engine.
However, direct injection gasoline engines can encounter problems different from those of the conventional engines due to the direct injection of gasoline into the combustion chamber. One of these problems is related to the smoke exhausted mainly from the part of the mixture in which the gasoline is excessively rich, upon the stratified combustion. The amount of soot produced is greater than that of a conventional MPI engine, thus a greater amount of soot can enter the lubricating oil through combustion gas blow by.
There are a number of technical issues to be resolved with DIG technology, and one of them is injector performance with different gasoline fuels on the world market. Being located in the combustion chamber, DIG injectors are exposed to a much harsher environment than conventional engines with port fuel injectors (PFI). This more severe environment can accelerate fuel degradation and oxidation to form deposits.
DIG technology promises about a third less carbon dioxide emissions than comparable conventional multi-port injection. This is achieved with a 10-15% improvement in fuel consumption when operating in the homogeneous mode, and up to 35% when operating in the lean stratified mode. Fuel economy benefits also translate into fossil energy conservation and savings for the consumer. In addition, the DIG operation platform facilitates up to a 10% power increase for the same fuel burned in the equivalent MPI configuration.
Current generation DIG technologies have experienced deposit problems. Areas of concern are fuel rails, injectors, combustion chamber (CCD), crankcase soot loadings, and intake valves (IVD). Deposits in the intake manifold come in through the PCV valve and exhaust gas recirculation (EGR). Since there is no liquid fuel wetting the back of the intake valves, these deposits build up quite quickly.
Injector deposits in DIG engines restrict fuel flow and alter spray characteristics of the injectors. Low levels of fuel flow restriction can be compensated for by engine control electronics. However, high levels of flow restriction and any level of spray distortion cannot be adequately controlled electronically. In PFI engines, the cut-off point, as defined by the U.S. Environmental Protection Agency, for injector flow restriction is 5% for any one injector when tested in accordance with ASTM D 5598-94. This is because spray distortion is not much of an issue. In DIG engines, on the other hand, charge flow characteristics in the cylinder are critical to the calibrations that go into driveability, fuel economy, and emissions. In-cylinder charge motion in DIG engines is very sensitive to injector spray distortion. For this reason, DIG injector flow restriction cut-off point may be much lower than the 5% level assigned to PFI injector performance.
Fuel related deposits in direct injection gasoline (DIG) engines are an issue of current interest since this technology is now commercial in Japan and Europe. Fuel injector performance is at the forefront of this issue because the DIG combustion system relies heavily on fuel spray consistency to realize its advantages in fuel economy and power, and to minimize exhaust emissions. A consistent spray pattern enables more precise electronic control of the combustion event and the exhaust after-treatment system.
There are numerous references teaching fuel compositions containing manganese compounds, for example, U.S. Pat. Nos. 5,551,957; 5,679,116; and 5,944,858. However, none of these references teach the use of fuel compositions containing manganese compounds in direct injection gasoline engines or the impact manganese compounds have on deposits in these engines.